This project from the Johns Hopkins University Department of Psychiatry in response to an NIMH Request for Applications seeks to develop a Diagnostic Center for Linkage Studies of Bipolar Affective Disorder. The project will be part of a cooperative agreement program involving active collaboration of NIMH staff and other diagnostic centers. The project will aim to develop, in the context of the collaboration, an appropriate plan for use of small families with highly informative family structures for linkage studies, to find and recruit 66 such bipolar families to the study, to develop and carry our clinical diagnostic protocol to classify the affected and unaffected phenotypes in the bipolar families, and to collect and ship to a central facility blood samples for lymphocyte transformation into permanent cell lines for DNA based linkage studies.